Stream - understand failbit

**Scatman** · 09-13-2020

Hi all,

i have created a text file:

Code:

100
200
three hundred
400

my goal is to output at the end : 100, 200, 400. which is worked with the following code:

Code:

while (true) {
            if (input >> num) {
                cout << num << " - ";
            }


            else if (input.eof()) {
                break;
            }


            else if (input.fail()) {
                input.clear();
                input.ignore(numeric_limits<streamsize>::max(), '\n');
            }
        }

but if i have a text file like this:

Code:

100
200
three 300
400

how should i modify the ignore function, that it does not discard the whole line , but only the word "three", so that i output : 100, 200, 300, 400

**Sir Galahad** · 09-13-2020

You could use getline() to read each line, split it by spaces, and then a stringstream object to extract valid values.

The real question though is why are you even trying to make sense of bad input? Seems to me it would make more sense to report an error and exit in such cases.

**Scatman** · 09-13-2020

Thanks for the hints, i will try it
i am not trying to make sense of anything, it was just for the sake of exercise (how would i solve if i had to

)

**laserlight** · 09-13-2020

Originally Posted by Scatman

i am not trying to make sense of anything, it was just for the sake of exercise (how would i solve if i had to )

That is what you're trying to do though: make sense of the input according to certain rules. When you're just allowing for one number per line, it is easy to be lax, but if you're trying to interpret a number on a line that may contain other things rather than just considering that to be invalid input, you should be more careful. The thing then is to be absolutely clear as to what are those rules. For example, what about:

Code:

three300

or

Code:

three300zero

or

Code:

three 300 five 500

Do you allow negative numbers?

So, depending on what rules you want to use, the exact approach you take to parsing for the number might differ.

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